Containers for numerous materials, such as drug doses and the like, are formed from such materials as metallic foils, including aluminum foil, molded plastics and the like. These containers may be formed with a generally planer lip at the top thereof to accept a closure thereon by either adhesive bonding or heat sealing. One such container is that disclosed in U.S. Pat. Nos. 3,695,084 and 3,850,340, which are assigned to the assignee of the present invention and which are incorporated herein by reference.
Such containers have in the past been covered by generally planer closures which themselves may be formed of metallic foils, such as aluminum foil, which are coated with either adhesive bonding material or a heat sealable coating at their peripheral edges to be affixed to the generally planer lip of the container body.
A problem with the employment of such planer flexible lids is the tendency for failure of the adhesive bond or heat seal along the lip of the container. Such failure results in the leakage of the contents within the container and, especially in drug and food uses, in contamination of the product so as to make the product unsuitable for sale and use. Also, failure of this seal may result in evaporation of the product held by the container and/or a change in the characteristics of the product.
These failures may occur from either or both of two separate conditions. First, leakage may occur due to seepage of the product within the container between the container lip and the closure. Second, leakage may occur in containers holding products under conditions of elevated temperature. As the temperature increases in the surroundings of the container, pressure may build up within the container. This pressure may become sufficient to overcome either the adhesive bond or the heat seal between the lip of the container and the closure and cause failure of the seal at that point. In either of these situations, such leakage results in an unacceptable container for sale or use. It is desirable, therefore, to provide a container closure for such flat lipped containers which may be either adhesively bonded or heat sealed to the generally planer lip of the container and which reduces substantially the failures caused by leakage, whether the leakage be due seepage or increased pressure within the container.